Surface treatment with energetic ions is essential in semiconductor processing, MEMS and MEMS manufacturing, pattern transfer technologies, hard coatings, etc.
Ion bombardment is employed in a variety of fields including cleaning, activating the surface of a substrate, modifying wettability, enhancing hardness, depositing various films, doping semiconductors by ion implantation, etc.
Typically, all ion processing techniques may be classified into the following two types.
The first type is one wherein an ion beam is extracted from an ion source and radiated onto a substrate placed at a predetermined distance away from it in a vacuum chamber.
This type separately or simultaneously transports the ion beam and the substrate in order to attain desired results.
As such, the ion charge may be neutralized by an auxiliary electron emitter.
Examples of the corresponding techniques include ion beam assisted deposition, ion beam etching or milling, and ion beam implantation.
The second type provides an apparatus wherein a workpiece is placed in a plasma atmosphere and electrically biased to a predetermined negative potential.
As such, ions are accelerated within the sheath formed in the front of the workpiece. To this end, DC, RF, and pulsed bias may be used.
This technique category includes PVD, PECVD, PI3D, RIE and so on.
Meanwhile, ion etching, also called ion milling, is important varieties of ion processing.
This is based on surface sputtering by energetic ions.
The important feature of ion sputtering is the nonlinear dependence of the sputtering rate on the angle of incidence of the ions, as shown qualitatively in FIG. 1.
Furthermore, ion sputtering may be applied to both physical and reactive processes.
The numerous applications of ion milling include semiconductor processing, formation of nanostructures, surface texturing, and surface smoothing.
Ion beam processing, corresponding to an advanced emerged technique, is used as a final step in the manufacturing of optical components.
Surface smoothing applications include reducing the micro-roughness on critical interfaces for optical components and high-power devices, or sample preparation in SIMS and TEM.
Typically plasma milling using normal ion incidence is uniformly carried out in a direction perpendicular to a substrate and is thus adapted for etching to form a pattern, and is not suitable for surface polishing that selectively removes protruding portions to reduce surface roughness.
In order to solve such problems, substrate tilting or rotating is commonly used in plasma milling that uses normal ion incidence (FIGS. 2 and 3).
For example, FIG. 2 shows the ion beam etching of a cylindrical workpiece, in which a ribbon ion beam travels from a linear ion source into a vacuum chamber along the axis of a workpiece 100 that is rotating.
FIG. 3 shows the ion beam etching of a planar workpiece.
As such, a circular ion beam emitted from an ion source is directed onto a workpiece 100 that is rotating in a state of being tilted at a predetermined angle in the vacuum chamber.
As seen in the drawing, an electronic gun functions to neutralize the charged ions.
Examples of commercial ion milling machines include Model 691 Precision Ion Polishing System available from Gatan Inc., Model 1010 Ion Mill available from Fischione Instr., and IonScan 800 Polishing Fault Correction System available from Roth & Rau AG.
Forming a pattern on the nanometer scale requires surface polishing to ones of nm or less.
Chemical mechanical polishing (CMP) is mainly utilized for polishing planar Si wafers in the semiconductor industry.
However, CMP cannot be applied to 3D substrates.
Applications requiring 3D substrates include for example photoreceptor drums used in electrophotographic machines.
Technologies which are recently received attention, like nano pattern transfer, may have many advantageous using 3D substrates, in particular, cylindrical substrates.
Large cylindrical nanostampers resulting from such substrates may be utilized as a key component of next-generation displays.
However, machines able to polish the large cylindrical workpiece to the desired level have not yet been introduced.
The ribbon ion beam emitted from a linear ion source may be applied to surface smoothing of a large workpiece. However, the productivity of this method is limited.
Using two or more ion sources simultaneously is devised but is problematic because the system becomes complicated, the machine price may increase, and respective components are less reliable because of interference between the ion sources.